I use different ways to send events to Google Analytics on my website. Some user interface interations sends using ga.js but some user actions (eq.: succesful auth or transaction) is possible to send only from server-side (PHP) using measurment protocol.
Events are both successfully sent and come to GA, but there's no link between JS and PHP events. For example, user entered website, clicked some buttons (stats sent by JS) and made a transaction (stats sent by PHP). After that i see JS events linked to one session but PHP event isn't linked. It just displayed as separate event.
What information should i store and pass to measurment protocol to have that events linked?
You need to send the client id (as set in the ga cookie, because this is the key GA uses to group visits into sessions) and possibly the user ip override and user agent override.